While few non-gamers have heard of Twitch, the site has 55 million unique monthly viewers - roughly on par with ESPN's Web traffic - who log in to learn strategies from their favorite pro video gamers and to watch big-jackpot tournaments in the burgeoning field of electronic sports, known to gamers as e-sports.

And that viewership - especially younger gamers who might choose to watch a "League of Legends" video game tournament over "Sunday Night Baseball" - is a big reason Amazon paid a premium to beat out Google.

"It's an audience that is really difficult to get access to, a group that is difficult to read," said tech analyst Brian Blau of Gartner Research.

On Monday, Seattle's Amazon agreed to buy Twitch for $972 million in cash - the largest acquisition in company history - in a deal expected to close later this year. According to sources familiar with the terms, the value inflates to $1.1 billion with employee retention incentives.

The deal trumped Google's widely reported $1 billion-plus offer, which would have added Twitch to its YouTube division. A published report in May said the Google deal was done, but other reports indicated the Mountain View search giant had qualms about potential antitrust problems.

There were rumors and "crazy leaks" about potential deals that were not all accurate, said Bessemer partner Ethan Kurzweil. "We can't comment on other interests Twitch might have had other than to say we found a great fit with Amazon, and Amazon made a compelling offer."

While online retailing doesn't by itself fit with gaming, Amazon is trying to increase its overall reach with entertainment content such as streaming movie and TV service rivaling that of Netflix, original programming and a game development studio. And Amazon does sell video games.

Twitch worked with game developers to add live online streaming to their titles, but received a big boost in the past year when Sony's PlayStation 4 and Microsoft's Xbox One home-video-game consoles integrated Twitch directly.

So with those factors, adding Twitch's gamer audience would have only added an "incremental bump" for YouTube, but could become a "kick-starter" for profits for Amazon, Blau said.

Michael Frazzini, Amazon Games vice president, said the big purchase price "shows the commitment we have to the games industry" and the "future of what Twitch can become."

"We think e-sports are going to be a rival or to be as big as any sport over time," he said.

Twitch emerged from Justin.tv, a San Francisco startup that created the idea of personal "lifecasting" in 2007, but failed to find a big audience. In 2010, executives pivoted the company toward video games and spun Twitch out as a separate brand in mid-2011. (Twitch recently shut down Justin.tv.)

Twitch CEO Emmett Shear said he chose Amazon because the two shared similar visions about the gaming industry and the company's strategy. He also said he was convinced by Amazon's commitment to keep Twitch autonomous.

"I get to continue being CEO and running the company, keep hitting everything we wanted to hit strategically and keep serving the community, but I get to do it faster and with more resources than ever before," he said.

Twitch will remain in San Francisco. The company has 170 employees, most based locally, but with some regional sales representatives around the world.

The deal is a big payoff for Bessemer Venture Partners, which led two previous investment rounds that totaled $35 million.

"For us, it's an excellent return in a very short period of time," Kurzweil said.